The invention relates to a method of raising a telescopic boom of a mobile crane having a luffing fly jib and having spatial boom guying.
Very high lifting heights and radii are frequently required. They go beyond the ranges of telescopic cranes. Luffing fly jibs are also mounted on the telescopic boom in such cases due to possible projecting edges. The luffing fly jibs can have very large lengths in this respect which can even project far beyond the length of the main boom itself.
With high projecting edges, lifting heights of up to 170 m are reached. Spatial guying at the telescopic boom is used for stabilization as a rule with such long boom systems. An eccentric fastening of the guying to the main boom tip has already become known from DE 20 2004 017 771 U1 which is likewise used in systems having such high lifting heights.
Large telescopic cranes are currently frequently designed so that they can be operated with spatial guying. They thus only reach the highest load torques with tensioned spatial guying in certain operating positions (for example, with a steep raising of the main boom). This operating position is actually frequently encountered on the use of a boom system having a main boom with a fitted luffing fly jib. The total stability of the main boom is greatly reduced without the tensioned spatial guying. It must be observed here that the spatial guying only extends over the main boom and an optionally present main boom extension. The luffing fly jib is in contrast held in the luffing plane by stay poles and optionally, with a special length, by additional intermediate guying means.
A corresponding crane boom according to the prior art is shown in FIG. 1. It has a telescopic boom 10 having a fitted luffing fly jib 12 (only shown schematically here). A guy rope 16 pivotally connected to the so-called raising trestles 14 as well as stay poles 18 which brace the luffing fly jib 12 and are connected to one of the raising trestles 14 at one end and to the free end 20 of the luffing fly jib 12 at the other end serve the luffing. So-called Y guying 22 is additionally provided which serves the spatial guying of the telescopic boom 10. Such a crane boom in accordance with the prior art is raised as follows:
1. First, the boom 10 and the spatial guying 22 are installed ready for operation, but naturally not tensioned. The telescopic boom 10 has not yet been extended to operating length.
2. Subsequently, the luffing fly jib is installed and is provided with at least one carriage so that it can travel on the ground.
3. Subsequently, the luffing fly jib 12 is connected to the almost horizontally positioned main boom 10. A possible main boom extension or an adapter such as are not shown in the representation in accordance with FIG. 1 is considered part of the main boom in the present description since it is fixedly connected to the main boom at the topmost telescopic section.
4. The inwardly telescoped main boom 10 is raised into a steep position, with the outer end of the luffing fly jib lying on the carriage at the base. For this purpose, the luffing fly jib can pivot around the pivotal connection points at the main boom 10.
5. Subsequently, the luffing fly jib is raised and set up in a steep position. The torque caused by the luffing fly jib is kept low by the steep positioning and the support friction in the telescope is advantageously reduced. At this time, however, the outer end of the boom system is free and has no form of support. The total guidance of the long boom system is provided by the main boom 10.
6. The main boom is then telescoped outwardly to the desired length. For this purpose, the boom section to be telescoped is in each case bolted to the telescopic cylinder.
7. After the expulsion, the bolting of the respective telescopic sections takes place, with the connection of the expulsion cylinder to the telescopic sections being released.
8. Finally, the spatial guying 22 is tensioned. The boom system now reaches its maximum working load.
9. In the raising method in accordance with the prior art, the weight of the total boom system bears on the telescopic cylinder and thus on the piston rod. The kinking forces acting on the piston rod and the torques acting on the support of the piston rod are highly relevant here. On the other hand, the total boom system has to be guided between the foot support and the head support of the telescope A to be expelled. The spacing of the two support points with respect to one another is reduced by the expulsion procedure, whereby an increasing support friction and thus higher telescopic cylinder forces occur.
It must furthermore be taken into account that at the end of the expulsion procedure the telescopic part 1 is expelled and this allows a relatively large side deformation of the boom system disposed above in the transverse direction to the boom in the non-bolted state. The total stability in the lateral direction is hereby no longer completely ensured. Due to the high lateral boom deformation, the loads on the pivotal connection piece and on the telescopic piece 1 become too high under certain circumstances.
The load on the boom system is the highest at step 5. Here, the maximum permitted lengths of the boom system, specifically those of the luffing fly jib, are limited by the forces and torques occurring in this installation procedure.